1. Field of the Invention
The invention relates generally to the field of communications. More particularly, the invention relates to radio frequency (RF) communications.
2. Discussion of the Related Art
Quadrature modulation techniques enable two independent signals to be combined at a transmitter, transmitted on the same transmission band, and separated at a receiver. The principle of quadrature modulation is that two separate signals, I and Q (In-phase and Quadrature phase), are modulated by using the same carrier wave frequency, but the carrier wave of signal Q is 90° out of phase relative to the carrier wave of signal I. After modulation, the resulting signals are summed and transmitted. Because of the phase difference, the I and Q signals can be separated from each other when the summed signal is demodulated at the receiver.
In practical applications, quadrature modulator circuit elements in the baseband (I and Q) channels may present electrical mismatch and produce undesirable DC offsets. Since the baseband paths are DC coupled, all individual DC offset errors may add up and produce a combined effect in the form a carrier feedthrough at the modulator output, degrading the quality of the transmission.
Present attempts to solve these problems have used separate, dedicated RF detectors to improve transmission quality, but this has resulted in increased system cost and higher current drain.